Batboard

I have a R2600 service monitor that has, over time, become unusable due to the buttons on the front panel becoming sticky with all sorts of old debris. ( I have no idea what all it might have as this unit has been sitting for quite some time. The unit seems to work ok in all modes, but I really need to be able to get the front panel off so that I can clean up the buttons to make it fully functional again. Does anyone have a set of instructions for how to safely remove the front panel for this purpose? I have searched for a service manual, but I am not even certain that it would contain that sort of information.
I have removed all knobs, and even the retaining nuts around the potentiometers that protrude through the panel, but it still seems to be firmly attached somehow.
Any help would be greatly appreciated ....